1. Field of the Invention
The present invention relates generally to a scanning probe microscope in combination with a confocal microscope and method for operating the resulting combination microscope. This invention more specifically relates to the use of a confocal microscope for detecting features in a wider field of view than that of the probe of the scanning probe microscope and then employing the probe microscope to examine the detail of features identified by the confocal microscope. The present invention also relates to the field of scanning probe microscopes, including probe microscopes that use either interference of light beam detection schemes or reflected beam position detectors.
2. Description of the Prior Art
The following U.S. Patents are incorporated by reference in their entirety for all purposes:
U.S. Pat. No. 5,861,550, issued 19 Jan. 1999, to David J. Ray for SCANNING FORCE MICROSCOPE
U.S. Pat. No. 5,874,669, issued 23 Feb. 1999, to David J. Ray for SCANNING FORCE MICROSCOPE WITH REMOVABLE PROBE ILLUMINATOR ASSEMBLY
U.S. Pat. No. 6,138,503, issued 31 Oct. 2000, to David J. Ray for SCANNING PROBE MICROSCOPE SYSTEM INCLUDING REMOVABLE PROBE SENSOR ASSEMBLY
U.S. Pat. No. 6,189,373, issued 20 Feb. 2001, to David J. Ray for SCANNING FORCE MICROSCOPE AND METHOD FOR BEAM DETECTION AND ALIGNMENT
U.S. Pat. No. 6,415,654, issued 9 Jul. 2002, to David J. Ray for SCANNING PROBE MICROSCOPE SYSTEM INCLUDING REMOVABLE PROBE SENSOR ASSEMBLY
U.S. Pat. No. 6,748,794, issued 15 Jun. 2004, to David James Ray for METHOD FOR REPLACING A PROBE SENSOR ASSEMBLY ON A SCANNING PROBE MICROSCOPE
U.S. Pat. No. 6,910,368, issued 28 Jun. 2005, to David J. Ray for REMOVABLE
PROBE SENSOR ASSEMBLY AND SCANNING PROBE MICROSCOPE U.S. Pat. Nos. 6,189,373, 6,415,654, 6,748,794, and 6,910,368 to Ray
Probe microscopes belong to a family of microscopes that use a small probe to detect and measure features in micrometer, nanometer and sub nanometer dimensions. Confocal microscopes, on the other hand, use apertures or a tightly focused laser beam in combination with an aperture or apertures for observing a sample surface. The present invention uses the advantages of each of these microscopes to obtain results that neither can individually obtain.
One type of probe microscope uses a light beam, often created by a laser, wherein the beam is directed at a reflecting surface on the free end of a cantilever. The cantilever surface opposing the reflecting surface includes a probe tip that senses some parameter of the sample surface. The combination of cantilever and probe are often referred to as a probe assembly. If the probe tip experiences a force, then the cantilever will bend or deflect. The deflection may be either toward the sample surface, if the force is attractive, or away from the surface, if the force is repulsive. The deflection may be measured by the beam of light is reflected from the reflecting surface of the cantilever. The position of the reflected beam may be determined by interposing an array of photo-detectors in the path of the reflected beam. Alternately the deflection of the cantilever may be detected by an interference detector that compares the light phase of the reflected beam with the light phase of the original beam. A probe microscope that exploits the phenomenon of a force exerted on the probe tip as a result of tip's proximity to another body is commonly known as a Scanning Force Microscope. In practice as the tip is moved in the X, Y plane the tip encounters different sample surface elevations. A computer is then used to display the cantilever deflection angle, or the positioning signal required to restore the cantilever to a specified deflection angle, as a function of the probe tip X, Y position. Using graphic techniques an image of the sample surface is recreated on the computer display.
If the forces detected are the inter-atomic forces between the atoms on the sample surface and the atoms of the probe tip then the probe tip is typically shaped like and acts in the fashion of a stylus as it is moved over the sample surface. A microscope that uses this phenomenon is typically referred to as an Atomic Force Microscope.
When used to image the topography of a sample, the scanning force microscope uses the finely pointed stylus to interact with a sample surface. Scanning force microscopes are typically used to measure the three dimensional topography of a sample surface. A scanning mechanism in the microscope creates relative motion between the stylus and the sample surface. Other classes of probe microscopes may use different types of probes to measure sample features other than topography. For example, the interaction of a magnetic probe with the sample may create an image of the magnetic domains of the sample. Scanning tunneling microscopes use a conductor with a sharp point and a small bias voltage to sense a sample surface which is then used to form an image of charge density.
Confocal microscopes operate by bringing, substantially, a point source of light to focus on a sample surface. An image of the point of light on the surface is then brought to focus at or near an aperture. The light then continues through the aperture on a path to a photo-detector that measures the intensity of the light. If the image of the approximate point source is in focus at the aperture, the aperture passes substantially all the light and the detector output is maximized. If the image is not in focus at the aperture the aperture vignettes a portion of the light and the detector output is less than if the aperture were located directly at the focus point of the light.
In modern confocal microscopes a disc containing a sequence of apertures may be used. By moving or rotating the disc, one aperture in the sequence passes light from a point on a specific location of the sample to the detector. When the disc is rotated the next aperture in the sequence of apertures passes light from different location on the sample to the detector. If the focus point of the light on the sample is above or below the actual surface of the sample then the detector will measure slightly less light passing through the aperture. The detector output at each aperture in the sequence can be processed by computer to create a data set that represents the relative intensity of the points on the sample. By changing the focus point of the light on the surface relative to the disc containing the apertures or by moving the disc to a slightly different Z position different planes of in focus light will be created at the apertures and a different set of surface data will result. The different data sets will essentially show all sample points that intersect the focus plane of any particular aperture as having greater intensity than sample points not in the focal plane of that aperture. A computer may be used to process the data sets to display a three dimensional image on the computer display device. The light source may be either a focused point source of white light or a focused source of laser or coherent light.
Each of these microscope types (confocal and probe) have advantages and disadvantages. Confocal microscopes can create images with very high resolution in the Z axis but typically have limited resolution in the X and Y axes to that of normal optical microscopes. Typically confocal microscopes have wider fields of view than probe microscopes. Probe microscopes on the other hand have greater resolution in the X, Y, and Z axes, but have fields of view that are restricted by the speed of the scan and the range of the scanning mechanisms.
U.S. Pat. Nos. 7,030,369, 6,339,217 and 6,515,277 to Kley address some aspects of the deficiencies of confocal and probe microscopes by describing an invention that directs light through a transparent probe or a portion of a transparent probe. In this case the light is recovered by a photo detector back through the probe. While this approach improves on the current art it does not completely solve the problems of scan speed and field of view. The apparatus described by Kley uses an X, Y translator to move the sample. As a consequence large samples pose technical problems in the form of the size and force that must be employed by the Kley sample translator in moving large samples at speeds that will result in acceptable scan times.
U.S. Pat. No. 5,581,082 to Hansma et. al. also describes an apparatus for combining a confocal and a probe microscope. Here again the sample moves while the scanning probe microscope and the confocal apparatus remain fixed in space. The same deficiencies as in the Kley patents are inherent in the Hansma et. al. microscope.
The present invention overcomes the deficiencies of the individual confocal and probe microscopes and leverages the advantages of both.